Tested, FIXED
as far as testing goes i run gpuz and it did not crash system, also ripped out both bios`s from slave and master and no crashes,
also then ran a 3d game twice, then waited 5 minutes then run GPUz and it did not crash system, ran perfect no lockups also bios ripping working though not sure if you touched that...

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2x His 7950s crossfire

As far as im concerned this build fixed the problem, i will do some more thorough testing and report final findings tomorrow, but as far as initial testing goes, you have fixed the issue.

thankyou

EDIT UPDATE : so far so good, more testing and no system locks.
i have noticed though on the 2nd GPU sensors ect its showing no GPU LOAD sensor only the first GPU is showing GPU LOAD sensor, and also VRM temps are showing 24c and 25c on both my cards, could it be becuse i have a custom pcb 7950s.... that has no VRM temp sensors or do you have a diagnostic dump to see if my cards do have them but not configured to the correct part of the gpus.

FINAL EDIT: no lockups, works though i would still like if its possible to get VRM temps on my cards.. and also 2nd card does not show GPU load in the sensors tab.

what about my questions mate, also i dont think he has the same issue as us
cause hwinfo was locking my system up as well basically doing the same as what your gpuz was doing...

that fixed build above though has solved the issue for me GPUZ no longer locks my system up at all and i have run it about 50 times lol even though hwinfo stick locks my system up if i run it after i have run a 3d game or if my system has been running for a wile before running it.